Conductivity and Hall-Effect Measurements on MBE GaAs Grown at Low Temperatures

We have performed Hall-effect and conductivity measurements on MBE GaAs layers grown at 200-400 oC, and annealed at temperatures up to 700 oC. A key element in the success of these measurements is removal of the substrate. Results include the first accurate measurement of mobility, which can be greater than 1000 cm2/V s in annealed material, and the discovery of a new, dense donor near EC - 0.45 eV, which is much shallower than the well-known EL2-like donor in this material. Annealing behavior of the electrical and optical properties can be quite complicated due to the existence of at least two donors as well as an acceptor, and two types of conductivity, hopping and band